In recent years, organic insulating materials used in adhesives, casting materials, sealants, molding materials, laminates, composite substrates and the like, mainly containing thermosetting resins have been required to have a high thermal conductivity for heat dissipation in keeping with trends toward the electrification of automotive power, the high integration of semiconductors, and the widespread use of LED lighting. Furthermore, the organic insulating materials are required to have a high thermal conductivity of, for example, 2.0 W/(m·K) or more because of the increase in temperature of usage environments.
Epoxy resin compositions having a mesogenic group are known as thermosetting resin compositions with high thermal conductivity. For example, Patent Document 1 discloses a thermosetting resin composition prepared by blending an epoxy resin (epoxy prepolymer) with a curing agent containing 1,5-diaminonaphthalene, the epoxy resin being produced by the reaction of a phenol compound such as 4,4′-dihydroxybiphenyl with an epoxy compound with a specific structure having a biphenyl group which is a mesogenic group.
Further, the above mentioned epoxy resin composition may contain filler such as metal oxides, metal hydroxides, or inorganic ceramics. It has been disclosed that for example, an inorganic powder filler such as alumina, silica, magnesium oxide, or aluminium hydroxide; a fibrous filler such as a glass fiber, a pulp fiber, a synthetic fiber, or a ceramic fiber; a colorant; or the like can be added into the composition.